NEW B Need Help on Output Tx Problem

[vangogh-hk]

I have just got my pair of Lundahl 1663PP Audio Transformer

(see http://www.lundahl.se/pdfs/datash/1663.pdf)

for my EL34 Project:

(http://www.lundahl.se/pdfs/claus_byr...fier_30wpp.pdf)

Not until I received the transformer, did I realize that the secondary coil of the transformer is only providing 8 Ohm output. (different from other audio transformer that they usually provide with more than one output such as 4-Ohm, 8-Ohm 16-Ohm tapping). As I am using a 4-Ohm speaker, could anybody advice how can I adapt the LL1663PP to match my 4-Ohm speaker.

Thank you very much for your help.

[dhaen]

Sorry to say that I would sell either sell the transformers, or change the speakers.

Just one possibility is to use an impedance matching transformer between the amp and speakers - useful if intend to change to 8 ohm speakers in the future... They are not too expensive, and you could sell those on later too.

[cerrem]

Looks like you have a problem......
If you hook up the 4 ohm to the secondary you will have 2.5K plate load.... The problem would be if the wire can handle the additional AC current.... I would guess it should based on a few assumptions...
Now you have to make the OUTPUT tubes "fit" the load-line, which is roughly 1/4 of 2.5K.....
If you get rid of the UL taps and run the Plates at 400V and the screens close to 400V , then the 2.5K plate load will fit just under the knee of the 0-bias curve..... The peak AC currents are a bit higher..... The flux density is well low in this case.... SInce it is music waveforms and you don't crank the amp to full volume you probably can get away with it..... See how it sounds...

Chris

[vangogh-hk]

I decided to go using my 5K to 8Ohm Lundahl output transformer (as I am going to diy a 8 ohm speaker as next project).

If my intention is to connect this EL34-PP power amp to my Ground Grid preamp or a single 5687 preamp. Do I need to modify the input stage (original circuit using EF86 as triod)?

Besides, I was recommended that with a 4 ohm speaker, I can use this 5K to 8 Ohm output transformer to build a 2A3-PP power amp instead of EL34-PP. Is it a feasible solution?

Thanks for advices.

[EC8010]

2A3 wants to see 5ka-a as well. What you could do, though, is to use two parallel pairs of 2A3 and load the transformer with your 4 Ohm loudspeaker.

[cerrem]

You are OK to use this transformer into a 4 ohm load using two EL34 valves....
If you connect the 8 ohm tap to 4 ohm speaker you will get 2.5K plate loading on the EL34 push-pull pair.....
This is a good fit, provided you do not use the screen taps..instead feed the screen voltage the traditional way and it should work out ...

Chris

[vangogh-hk]

Chris,

"This is a good fit, provided you do not use the screen taps.."

Does it means that I should not use the ultra linear tap from the output trasnsformer to feed into the 2nd screen of the EL34. What is the result if ultra linear connection is used instead.

"instead feed the screen voltage the traditional way and it should work out ..."
What is the traditional way of connection?(Sorry it is the first time I made a PP amp)

[cerrem]

What I ment was to not use the screen taps...tape them and tuck them out of the way...
Use a choke such like a 10H @ 50-100mA with a 100uF after it to feed the screens from the B+ .......
This would also feed the pre-driver stage...
Go to your page #15 in your booklet and look at that schematic..
Replace R22 with the 10H Choke and make C14 100uF if possible, if you can't then the 50uF will suffice....

Best Regards
Chris

[Dave Cigna]

Why the heck do they call this a 5K:8 transformer when the data sheet shows it as having a 24:1 winding ratio? That makes it 4.6k:8.

Lundahl is usually pretty good about getting the details right in their spec sheets.

Lundahl data sheets can be found at http://www.kandkaudio.com/datasheets.html

[cerrem]

Hey Dave....
It's been a long time....
Just look at cerrem and spell it backwards

Chris